1. Field of the Invention
The present invention relates to a process for etching films of an aluminum-based material by using two specific different gases.
2. Description of the Prior Art
It is known that films of an aluminum metal or an aluminum alloy can be etched to form wirings for use in integrated circuits particularly in the manufacture of semiconductors. For convenience, such film is referred to simply as an Al film.
In an industrial sector of wirings for integrated circuits of semiconductors, Al films of a multilayered structure combined with a metallic barrier layer have recently been reputed for their good resistance to migration and to contact. This structure is made up typically of a film of Al or an Al alloy such as Al-Si and a barrier layer of TiON-Ti, TiW or TiW-Ti disposed integral with a lower side of the film.
Attempts have also been made to laminate a reflection-inhibiting layer such as of TiON of an inorganic class on or over an Al film. The inhibiting layer compensates for immunity from lithographic pattern defects which may take place from surface reflection of the Al film.
To meet the foregoing requirements, a laminate shown in FIG. 3 has been proposed to be etched. Designated at 1 is a film of an Al-Si alloy with an Si content of about 1% by weight, and a barrier layer 2 is interposed between the film 1 and a substrate 5 such as SiO.sub.2. The barrier layer 2 is composed of a TiON layer 21 placed on a lower side or surface of the film 1 and a Ti layer 22 mounted on an upper surface of the substrate 5. An reflection-inhibiting layer 3 is disposed over the film 1, a TiON layer being here exemplified on which a resist mask 4 is positioned.
The composite material of FIG. 3, however, cannot be adequately processed by a mode of etching commonly employed to etch a single Al-Si film with good anisotropy. This is partly due to the reflection-inhibiting layer 3 being present between the resist mask 4 and Al-Si film 1 and partly due to the TiON and Ti layers 21, 22 being underneath the film 1. To be more specific, one-step or continuous etching is not applicable because the film 1 is necessarily overetched, as viewed in FIG. 2, under a set of conditions intended to etch the barrier layer 2.
FIG. 2 shows a structure resulting from etching the material of FIG. 3 on an electron cyclotron resonance (ECR)-etching system and under the following conditions.
gas: BCl.sub.3 /Cl.sub.2 =60/90 SCCM PA2 pressure: 16 mTorr PA2 microwave: 300 mA PA2 RF bias: 40 W
When the barrier layer 2 is satisfactorily etched, the Al-Si film 1 undergoes excessive etching owing to insufficient anisotropy and results in adverse undercutting. To solve this problem, Al films have been protected sidewise with deposits which may be generated from resist decomposition products upon exertion of incident ion energy to a greater extent. Although effective to improve anisotropy, such protection means is susceptible to the following drawbacks.
1. Etch selectivity is rendered small with respect to the resist and substrate.
2. In a step of over etching, both the resist and the resultant pattern at its side walls tend to involve objectionable sputtering arising out of the substrate. This in turn leads to a so-called after corrosion if a given etching gas contains a chlorine atom or atoms in the molecule Details as regards that corrosion are reported in "Semiconductors and Circuitry, 35th Symposium Prints", Pages 13-18, Article No. 3, December 1988.
Gases such as SiCl.sub.4 and the like which are capable of deposition are in common use in protecting Al films. However, these gases will in most cases put an etching chamber into a full deposition atmosphere, entailing particle dusting or contamination.